Cave diving instructor Brian Kakuk was guiding a diver in a blue hole south of Marsh Harbour a few years back when he spotted what appeared to be a turtle shell buried in the sediment about 60 feet deep.
Kakuk brought it up during a later dive and presented it to scientist Dick Franz of the Florida Museum of Natural History at the University of Florida.
"He freaked out," Kakuk said.
Turns out it was a near-perfectly preserved shell of an extinct land tortoise more than 2,500 years old - never previously identified.
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Said Franz: "This is totally beyond anything expected to occur, not only in the Bahamas but in the whole West Indian region."
Kakuk kept on diving in Sawmill Sink and several other nearby deep, water-filled caves and discovered more and more fossils - more than 40 complete skeletons of 3,000-year-old freshwater Cuban crocodiles; a flightless shorebird; an extinct cara cara, or vulture; a hutia, a large rodent found on some remote islands in the Bahamas; prehistoric owl pellets; a human bone.
The human bone was the youngest of the finds, at about 1,000 years old, according to Kakuk. He thinks there may be human and animal remains in many more marine caves throughout the Abacos and the rest of the Bahamas, most of which have never been explored.
"Nearly every inland hole we've dived in we've found this stuff," he said.
Kakuk is working with Franz, paleontologist and crocodile specialist Gary Morgan of the New Mexico Museum of Natural History and Nancy Albury, who runs a branch of the Bahamas National Museum in Abaco, to conserve and identify the fossils.
"They are the best preserved fossil vertebrates ever found in the Caribbean anywhere," Morgan said. "Eventually, it's going to be a Bahamas-wide project."
Kakuk says the fossils have been kept intact over the centuries by the peculiar water chemistry in the caves. The surface waters of the inland blue holes are fresh, giving way to saltwater down deep that flows from the ocean through underground passages. Hydrogen sulfide, from dissolved plants and other organic material, removes oxygen from the water and preserves the bones.
"I liken it to the La Brea tar pits of the Bahamas," Kakuk said, referring to a paleontological site in California.
Diving in the underwater caves, Kakuk uses a Megalodon rebreather because it generates fewer bubbles than open-circuit scuba gear. Bubbles disturb the centuries-old layers of sediment that protect the fossils. If too much sediment is dislodged, it can cost a diver his or her life, obscuring visibility and blocking the exit to the surface.
RICH IN FOSSILS
So far, Kakuk has dived 180 feet deep in Sawmill Sink to map 2,000 feet of passages.
"There's fossils in the ceiling, the floor, the walls," he said.
He has found crocodile skeletons and tortoise shells fairly close together at similar depths - indicating the two species probably co-existed. The crocs - an aggressive, endangered variety native to Cuban swamps - might have preyed on the tortoises. One of the shells bears deep teeth marks with bits of flesh still inside the holes.
Franz said the tortoise remains - never before discovered anywhere - are a native species similar to the giant land tortoise found in the Galapagos Islands off Ecuador. He said the animals lived in the Bahamas almost 2,000 years before humans appeared, and somehow became extinct.
One of the mysteries that has arisen from the finds is how freshwater crocodiles from Cuba made it across the ocean to live in the Bahamas long before people were around to relocate them.
"Maybe there was a hurricane or big flood and they got washed into the Florida Straits or Caribbean Sea," Morgan said. "Somehow they got there naturally. I bet the crocodiles show up in other places. There are other islands they presumably would have gotten to before Abaco."
10,000 YEARS OLD
The owl pellets, basically fossilized vomitus of whatever the birds ate, were found in deeper water in the sink. Morgan said these are much older than the reptile bones - possibly 10,000 years or more, when water levels worldwide were much lower and the cave would have been dry. Those remains have not been scientifically dated.
The scientists are optimistic they will be able to learn a lot more about the natural history of the Bahamas from Kakuk's discoveries.
Said Franz: "I think the potential is beyond our comprehension at this point. We should be able to reconstruct the past 10,000 to 12,000 years in the Bahamas - maybe longer."